Au–Hg–Ag phases have been described from a variety of metallogenic orebodies and the placer deposits derived from them. In many documented placer deposits, the phases typically occur intergrown as ‘secondary’ rims to primary Au–Ag grains. The origin of these rims has been ascribed to supergene redistribution reactions during deposition or to the effects of amalgamation (i.e. use of mercury) during mining for gold. Difficulties in determining compositions and crystal structures on such a small scale have made full characterisation of these phases problematic. This paper describes a new occurrence of these phases, found by accident during investigation of a historical concentrate of ‘osmiridium’ containing a number of gold grains from beach sands at Waratah Bay, in southern Victoria, Australia. The phases occur as rims to gold grains and are intergrown on a scale of tens of micrometres or less. Application of electron microprobe analysis (EPMA) and limited electron back-scattered diffraction (EBSD) was required to characterise them. These techniques revealed the presence of the approved mineral weishanite (Au–Hg–Ag) and a phase with compositional range Au2Hg–Au3Hg surrounding primary Au–Ag (electrum) containing trace amounts of Hg. EBSD analysis showed weishanite is hexagonal P63/mmc and Au2Hg to be hexagonal P63/mcm. Comparison with published data from other localities (Philippines, British Columbia and New Zealand) suggests weishanite has a wide compositional field. Textures shown by these phases are difficult to interpret, as they might form by either supergene processes or by reaction with anthropogenic mercury used during mining. However, in the absence of any historical evidence for the use of mercury for gold mining at Waratah Bay, we consider the formation of the Au–Hg phases is most probably due to supergene alteration of primary Au–Ag alloy containing small amounts of Hg. In addition to revealing some of the reaction sequences in the development of these secondary Au–Hg–Ag rims, this paper illustrates methods by which these phases can be more fully characterised and thereby better correlated with the Au–Hg synthetic system.

Au-Hg-Ag 相已在多种成矿矿体及其衍生的砂矿中得到描述。在许多有记录的砂矿床中，这些相通常作为原生金银颗粒的“次生”边缘共生。这些边缘的起源归因于沉积过程中的表生重新分布反应或金矿开采过程中的混汞效应（即使用汞）。在如此小规模上确定成分和晶体结构的困难使得这些相的全面表征成为问题。本文描述了这些相的新出现，是在对澳大利亚维多利亚州南部沃拉塔湾海滩沙子中含有大量金粒的“锇”历史精矿进行调查时偶然发现的。这些相以金颗粒的边缘形式出现，并以数十微米或更小的尺寸共生。需要应用电子微探针分析（EPMA）和有限电子背散射衍射（EBSD）来表征它们。这些技术揭示了已批准的矿物微山石 (Au-Hg-Ag) 的存在，以及成分范围为 Au 2 Hg-Au 3 Hg的相，围绕着含有微量汞的原生 Au-Ag（金金石）。 EBSD分析表明，微山石为六方晶系P 6 3 / mmc，Au 2 Hg为六方晶系P 6 3 / mcm。与其他地区（菲律宾、不列颠哥伦比亚省和新西兰）公布的数据进行比较表明，微山石具有广泛的成分范围。这些相显示的纹理很难解释，因为它们可能是通过表生过程或与采矿过程中使用的人为汞反应形成的。然而，由于没有任何历史证据证明 Waratah 湾使用汞进行金矿开采，我们认为 Au-Hg 相的形成很可能是由于含有少量汞的原生 Au-Ag 合金的表生蚀变所致。除了揭示这些次级 Au-Hg-Ag 环发展中的一些反应序列之外，本文还说明了可以更全面地表征这些相的方法，从而更好地与 Au-Hg 合成系统相关。